liblttng-ust/lttng-context-procname.c

   1 /*
   2  * (C) Copyright        2009-2011 -
   3  *              Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * LTTng UST procname context.
   6  *
   7  * Dual LGPL v2.1/GPL v2 license.
   8  */
   9
  10 #include <sys/prctl.h>
  11 #include <lttng/ust-events.h>
  12 #include <lttng/ust-tracer.h>
  13 #include <lttng/ringbuffer-config.h>
  14 #include <assert.h>
  15
  16 #define PROCNAME_LEN    17      /* includes \0 */
  17
  18 /*
  19  * We cache the result to ensure we don't trigger a system call for
  20  * each event.
  21  * Upon exec, procname changes, but exec takes care of throwing away
  22  * this cached version.
  23  */
  24 static char cached_procname[17];
  25
  26 static inline
  27 char *wrapper_getprocname(void)
  28 {
  29         int ret;
  30
  31         if (caa_unlikely(!cached_procname[0])) {
  32                 ret = prctl(PR_GET_NAME, (unsigned long) cached_procname,
  33                         0, 0, 0);
  34                 assert(!ret);
  35         }
  36         return cached_procname;
  37 }
  38
  39 void lttng_context_procname_reset(void)
  40 {
  41         cached_procname[0] = '\0';
  42 }
  43
  44 static
  45 size_t procname_get_size(size_t offset)
  46 {
  47         size_t size = 0;
  48
  49         size += PROCNAME_LEN;
  50         return size;
  51 }
  52
  53 static
  54 void procname_record(struct lttng_ctx_field *field,
  55                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  56                  struct ltt_channel *chan)
  57 {
  58         char *procname;
  59
  60         procname = wrapper_getprocname();
  61         chan->ops->event_write(ctx, procname, PROCNAME_LEN);
  62 }
  63
  64 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  65 {
  66         struct lttng_ctx_field *field;
  67
  68         field = lttng_append_context(ctx);
  69         if (!field)
  70                 return -ENOMEM;
  71         if (lttng_find_context(*ctx, "procname")) {
  72                 lttng_remove_context_field(ctx, field);
  73                 return -EEXIST;
  74         }
  75         field->event_field.name = "procname";
  76         field->event_field.type.atype = atype_array;
  77         field->event_field.type.u.array.elem_type.atype = atype_integer;
  78         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
  79         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = lttng_alignof(char) * CHAR_BIT;
  80         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = lttng_is_signed_type(char);
  81         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
  82         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
  83         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
  84         field->event_field.type.u.array.length = PROCNAME_LEN;
  85         field->get_size = procname_get_size;
  86         field->record = procname_record;
  87         return 0;
  88 }